Netty 是基于 Java NIO 的异步事件驱动的网络应用框架，使用 Netty 可以快速开发网络应用，Netty 提供了高层次的抽象来简化 TCP 和 UDP 服务器的编程，下面看看Netty 实现HTTP、TCP、UDP和WebSocket编程的使用。

1. HTTP编程

代码如下：

public class HttpServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new HttpServerInitializer());

            Channel ch = b.bind(8080).sync().channel();
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

2. TCP编程

代码如下：

public class TcpServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)
             .channel(NioServerSocketChannel.class)
             .childHandler(new TcpServerInitializer());

            Channel ch = b.bind(8888).sync().channel();
            ch.closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

3. UDP编程

代码如下：

public class UdpServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
             .channel(NioDatagramChannel.class)
             .handler(new UdpServerInitializer());

            Channel ch = b.bind(9999).sync().channel();
            ch.closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

4. WebSocket编程

代码如下：

public class WebSocketServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new WebSocketServerInitializer());

            Channel ch = b.bind(8080).sync().channel();
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}